This Week in Science

Science  20 Feb 2015:
Vol. 347, Issue 6224, pp. 836
  1. Animal Evolution

    Getting bigger all the time

    1. Sacha Vignieri

    Marine mammals such as this manatee have evolved to be larger over time


    In today's world, many animal species are large, with even larger species only recently extinct, but the first animals to evolve were tiny. Was this increase in size due to active selection or to some more random process? Heim et al. test the classic hypothesis known as Cope's rule, which posits that there is selection for increasing body size. They analyzed a data set that spans over 500 million years and includes more than 17,000 marine animal species. In support of Cope's rule, body volumes have increased by over five orders of magnitude since the first animals evolved. Furthermore, modeling suggests that such a massive increase could not have emerged from a random process.

    Science, this issue p. 867

  2. Spatial Navigation

    Are we heading in the right direction?

    1. Peter Stern

    Some neurons, called grid cells, discharge at multiple locations to form a regular pattern that represents the animal's environment. These cells use information about the animal's running speed and direction of movement to constantly update its location. The so-called head direction cells provide the direction-of-movement signal. Winter et al. recorded neuronal activity in awake behaving rats. When they disabled the input from the head direction cells, the grid cells lost their normal function. These findings provide experimental confirmation of theoretical predictions that grid cells will no longer exhibit their characteristic firing pattern when the head direction signal is disturbed.

    Science, this issue p. 870

  3. Global Food Security

    China addresses food and environment security

    1. Gary E. Machlis

    Chinese leaders are addressing the difficult challenge of meeting growing demands to produce more food in sustainable ways. Lu et al. describe current air, water, and soil conditions in China, along with changing food security demands. They argue that national policies must rely on a science-based “ecological red line” that balances food security and safety with sustainable management of soil, air, water, and biodiversity resources. The scientific community will need to work with policy-makers to ensure that national, provincial, and local land-use practices are data-driven. Land-use programs should be created and enforced with long-term consequences in mind.

    Science Advances 10.1126/sciadv.1400039 (2015).

  4. Kinase Dynamics

    Evolution of dynamics affects function

    1. Valda Vinson

    The drug Gleevac inhibits Abl kinases and is used to treat multiple cancers. The closely related Src kinases also play a role in cancer but are not inhibited effectively by Gleevac. Nevertheless, Gleevac-bound structures of Src and Abl are nearly identical. Based on this structural information and protein sequence data, Wilson et al. reconstructed the common ancestor of Src and Abl. Mutations that affected conformational dynamics caused Gleevac affinity to be gained on the evolutionary trajectory toward Abl and lost on the trajectory toward Src.

    Science, this issue p. 882

  5. Optics

    Slowing down light with added structure

    1. Ian S. Osborne

    We are taught that the speed of light in free space is one of the universal physical constants: c. Giovannini et al. now show that there are certain conditions under which such certainty can be broken (see the Perspective by Sambles). Adding spatial structure to an optical beam of single photons reduced the speed of light. The magnitude of the decrease depended on the complexity of the structure imprinted onto the photons.

    Science, this issue p. 857; see also p. 828

  6. Galaxy Evolution

    Finding the necessary negative feedback

    1. Margaret M. Moerchen

    The evolution of galaxies seems to be tied to the growth of the supermassive black holes at their centers, but it's not entirely clear why. Models have suggested a mechanism in which the growth of the black hole results in an outflow of gas that interrupts star formation. However, evidence for enough of this negative feedback has been lacking. Nardini et al. now see a signature in x-ray spectra of a strong persistent outflow in the quasar PDS 456. They estimate a broad solid angle spanned by the wind that enables a far greater impact on the host galaxy than narrower jet outflows.

    Science, this issue p. 860

  7. Photochemistry

    The dark side of melanin exposed

    1. Paula A. Kiberstis

    DNA damage can continue after sun exposure has ended


    Sun worshippers may have more to worry about than the DNA damage that occurs while they're relaxing on the beach. It seems that the DNA photoproducts responsible for cancer-causing mutations in skin cells continue to be generated for hours after sunlight exposure. Premi et al. find that a key mediator of this delayed damage is melanin, a pigment thought to protect against cancer (see the Perspective by Taylor). They propose a “chemiexcitation” model in which reactive oxygen and nitrogen species induced by ultraviolet light excite an electron in melanin fragments. This energy is then transferred to DNA, inducing the same damage as ultraviolet light, but in the dark. Conceivably, this energy could be dissipated by adding quenchers to sunscreens.

    Science, this issue p. 842; see also p. 824

  8. Transition States

    A transition state holds a pose

    1. Phil Szuromi

    The transition state of a chemical transformation is inherently fleeting because the structure is high in energy. Nonetheless, Pearson et al. trapped a classical example of a bond rotation transition state using a modified protein (see the Perspective by Romney and Miller). The biphenyl molecule passes through an energy maximum when its rings rotate through a parallel position. A pocket within the editing domain of threonyl–transfer RNA synthetase was modified to stabilize parallel biphenyl rings, allowing further characterization of this normally transient structure.

    Science, this issue p. 863; see also p. 829

  9. Cancer

    How Pez dispenses with metastasis

    1. Leslie K. Ferrarelli

    Tumor cells have greater numbers of growth-promoting receptors on their surface and release factors that promote metastasis. Belle et al. found that the protein tyrosine phosphatase PTPN14 (also called Pez) prevented receptors from moving to the cell surface and pro-metastatic factors from being released. Mice with breast cancer xenografts that lacked Pez had larger tumors and more metastases.

    Sci. Signal. 8, ra18 (2015).

  10. Nanomaterials

    Valency and bonding on a larger scale

    1. Marc S. Lavine

    In molecular systems, valency describes the number of bonds an atom can make with its neighbors. Larger objects such as colloids can be linked together to make connected structures in which the number of connections, or valency, is controlled by the central object. Jones et al. review the two main approaches to creating stiff bonds, based on DNA-based materials synthesis. These approaches allow the construction of molecular-like objects from building blocks much larger than single atoms.

    Science, this issue 10.1126/science.1260901

  11. Disease Networks

    A network approach to finding disease modules

    1. Barbara R. Jasny

    Shared genes represent a powerful but limited representation of the mechanistic relationship between two diseases. However, the analysis of protein-protein interactions has been hampered by the incompleteness of interactome maps. Menche et al. formulated the mathematical conditions needed to allow a disease module (a localized region of connections between disease-related proteins) to be observed. Only diseases with data coverage that exceeds a specific threshold have identifiable disease modules. The network-based distance between two disease modules revealed that disease pairs that are predicted to have overlapping modules had statistically significant molecular similarity. These similarities encompassed their protein components, gene expression, symptoms, and morbidity. Molecular-level links between diseases lacking shared disease genes could also be identified.

    Science, this issue 10.1126/science.1257601

  12. Structural Biology

    An interaction that guides cell fate

    1. Valda Vinson

    Notch signaling is important in cell fate determination in mammals. Signaling is initiated when the extracellular domain of the transmembrane Notch protein on one cell binds to a surface ligand on another cell. Luca et al. report the crystal structure of the interacting regions of Notch and the Delta-like ligand DLL-4. The Notch protein is modified by O-linked glycan addition, and this is required for signaling. The structure shows two interaction interfaces. A glycan anchors the less conserved interface, which potentially provides a flexible way of regulating Notch interactions during development.

    Science, this issue p. 847

  13. Quantum Engineering

    A way to induce quantum stability

    1. Ian S. Osborne

    Dynamical systems, whether classical or quantum, usually require a method to stabilize performance and maintain the required state. For instance, communication between computers requires error correction codes to ensure that information is transferred correctly. In a quantum system, however, the very act of measuring it can perturb it. Leghtas et al. show that engineering the interaction between a quantum system and its environment can induce stability for the delicate quantum states, a process that could simplify quantum information processing.

    Science, this issue p. 853

  14. Insulin Granules

    Too hungry to eat, too hungry not to eat

    1. Stella M. Hurtley

    Pancreatic beta cells, the source of insulin in response to food, employ an unusual mechanism to adapt to nutrient depletion. Goginashvili et al. found that starvation of beta cells induced selective degradation of newly formed insulin granules through their fusion with lysosomes, the cell's garbage disposal units (see the Perspective by Rutter). The nutrient sensor mTOR is recruited to these lysosomes, leading to its local activation and the suppression of autophagy—a process by which cells “eat” their own constituents. Protein kinase D, a major regulator of insulin granule biogenesis, controls this granule degradation in response to nutrient availability. Thus, unlike most other cells, autophagy is not the strategy of choice in beta cells to adapt to starvation.

    Science, this issue p. 878; see also p. 826

  15. Drug Mechanism

    Drugs can compete for vitamin K

    1. Megan Frisk

    Patients on warfarin—a commonly prescribed anticoagulant—are warned against eating leafy greens because they harbor loads of vitamin K, which interferes with the drug's activity. Takada et al. now show that Niemann-Pick C1-like 1 (NPC1L1), a cholesterol transporter, complicates this picture even further through its role in vitamin K absorption. Warfarin activity was enhanced in animals taking the cholesterol-lowering drug ezetimibe, which acts on NPC1L1, because vitamin K was not absorbed properly. Giving the animals vitamin K returned warfarin activity to normal levels . In patients, too, the warfarin action was boosted when it was taken with ezetimibe. This drug-drug interaction is an important consideration when warfarin is prescribed to patients taking ezetimibe (or similar drugs that alter vitamin uptake).

    Sci. Transl. Med. 7, 275ra23 (2015).

  16. Evolutionary Ecology

    Mother knows best

    1. Sacha Vignieri

    Dynamic natural environments are challenging places to start life. In many species, however, the environment the mother lives in can actually shape the environment in which her offspring grow. Such maternal effects facilitate the exchange of important environmental information across generations. Duckworth et al. show that a mother's physiological responses to her environment can convey more complex information than we thought (see the Perspective by Dantzer). Female western bluebirds deposit more androgens in their eggs when competition for nest sites increases. This results in more-aggressive male chicks that are more likely to move on and colonize new, less crowded habitats.

    Science, this issue p. 875; see also p. 822

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